Power supply circuits

ABSTRACT

The filaments of a plurality of vacuum tubes and the primary winding of a transformer are connected in series across an AC energizing source. The voltage drop across the primary winding is equal to the difference in the voltage of the AC source and the rated voltage drop across the series connected filaments. The voltage developed across the transformer secondary winding is coupled to utilization means such as the filaments of the kinescope for energizing the same.

United States Patent Inventor Seymour Reich Livingston, NJ. App]. No. 867,451 Filed Oct. 20, 1969 Patented Dec. 7, 1971 Assignee RCA Corporation POWER SUPPLY CIRCUITS 5 Claims, 1 Drawing Fig.

US. Cl 315/96, 315/97, 315/99, 315/106, 315/256, 315/1, 328/268 Int. Cl Hillj 31/01) Field of Search 315/94, 95,

96,97,99, 105,49, 64, 66,106,177,178, 179, 192, 254, 256; 330/1 15, 206; 328/268,270; l78/dig. ll

[56] References Cited UNITED STATES PATENTS 2,252,057 8/1941 Blessing 328/279 X 3,141,994 7/1964 Hornfeck et a1. 315/96 Primary Examiner-John Kominski Anorney--Eugene M. Whitacre ABSTRACT: The filaments of a plurality of vacuum tubes and the primary winding of a transformer are connected in series across an AC energizing source. The voltage drop across the primary winding is equal to the difference in the voltage of the AC source and the rated voltage drop across the series connected filaments. The voltage developed across the transformer secondary winding is coupled to utilization means such as the filaments of the kinescope for energizing the same.

POWER SUPPLY CIRCUHTS This invention relates to a power supply circuit configuration for the heaters or filaments of vacuum tubes.

lt is known to use series filament string arrangements which include a series droppingresistor to accommodate the difference in potential between the total filament string voltage drop and the magnitude of the AC source. Because of the relatively largefilament current required by present day vacuum tubes, the value of the series dropping resistor necessitated the use of a large power rated component in order to provide the requisite voltage drop at the desired series current.

In the case of a television receiver, a further requirement is supplying filament power to operate the electron gun of the kinescope employed therein. Desirably, the kinescope filaments should be isolated from other circuits in the receiver which, for example, may operate at different voltage levels. To accommodate such isolation, a separate filament transformer may be provided for stepping the AC line voltage down the voltage (i.e. to 6.3 volts) required by the kinescope filament.

A circuit in accordance with one embodiment of the invention includes the filaments of a plurality of vacuum tubes connected in series with the primary winding of a transformer.

The primary winding is selected such that it has an impedance at the requisite series filament current and at the frequency of the AC source to provide a voltage drop thereacross approximately equal to the difference between the AC source voltage and the total desired or rated series filament string voltage.

The secondary winding of the transformer is coupled to utilization means, such as the filaments of a kinescope, for energizing the same while desirably isolating the kinescope filaments from other circuits of the receiver.

Reference is made to the following specification when read in conjunction with the accompanying diagram, the sole FIGURE of which is a schematic diagram partially in block form of a television receiver including a series filament string embodying the invention.

A television receiver include a kinescope 11 and a plurality of vacuum tubes, not shown, which have heaters or filaments l4, 115, 16, and 117. The filaments 14-47, and the primary winding of a transformer are connected in series across an (AC) alternating current power source which may comprise the line voltage. The secondary winding of the transformer 20 is connected to energize the filament or filaments of the kinescope 11.

The primary winding is selected to have an impedance at the series filament current and the AC line potential frequency to provide the voltage drop equal to the difference between the magnitude of the voltage of the AC line and the sum of the rated or desired voltage drops across the series filament string.

Because the drop across the primary winding of the transformer 20 is lower than the AC line voltage, the transformer may have less turns, less copper and less iron than those filament transformers directly energized from the AC line voltage. Where the voltage drop across the primary windings of the transformer 20 is more than the usual 6.3 volts required in the secondary for operation of the kinescope filaments, the transformer 20 provides a voltage stepdown from primary to secondary accompanied by a current step-up. Most conventional vacuum tubes require less filament current than does a kinescope and hence the current step-up is compatible with conventional kinescope operation. if the current step-up is too great, a capacitor 211 may be placed across the primary winding 20 to divert current from the primary and therefore change the effective current transformed to the secondary. in a similar manner, a current diverting resistor or capacitor may be utilized at the secondary winding of the transformer to assure proper filament current flow in the kinescope Ill.

Alternatively, if the voltage drop across the primary winding of transformer 20 is about 6.3 volts, then the transformer 20 may have a l-to-l turns ratio and the secondary current will equal the primary current permitting the use of those kinescopes which require about the same filament current as the vacuum tube filaments 14 to 18. In the circuit shown, the kinescope filaments are isolated from the receiver power supply circuits; and, if desired, a fixed DC potential may be applied to the terminal 22 to protect. the kinescope against heater-to-cathode voltage breakdown.

The circuit configuration described protects the kinescope from voltage variations. For example, during turn-on of the receiver, the resistance of the filament string when cold is low and hence there is a current surge through the filaments. This current surge saturates the transformer 20 and limits the amount of secondary voltage developed during this condition, thus protecting the kinescope. By connecting the transformer in'the ground side of the line in the manner shown, voltage variations and spikes which may be present on the AC line voltage are attenuated by the divider formed between the filaments'and the primary winding of transformer 20.

In a similar manner kinescope arcs which tend to take a path through the transformer windings back towards ground would be severely attenuated by the transformer as the frequency response of the transformer need only be about 60 cycles, (for domestic receivers). As is known, an arc possesses a relatively fast rise time and a relatively narrow duration and may be represented by a series of high-frequency components which would be attenuated due to the low-frequency characteristics of the transformer.

What is claimed is:

1. In a television receiver employing a plurality of vacuum tube circuits having the filaments of each of said vacuum tubes connected in series with one another between first and second terminals of a source of AC potential for energizing said filament string, said source having a voltage magnitude greater than that required by the voltage drop across said filament string, said receiver including a kinescope having a filament which desirably is isolated from said AC source, the improve ment therewith comprising:

a. a transformer having a primary winding and a secondary winding, said primary winding having an impedance so that the voltage developed thereacross is approximately equal to the difference between said voltage magnitude of said source and said voltage drop across said filament string, said primary winding being connected in series with said filament string, and

b. means coupling said secondary winding of said transformer to said filament of said kinescope for energizing said filament while isolating said filament as desired due to said transformer action, whereby said kinescope filament is further protected from transients which appear on said AC source.

2. In combination:

a. a source of alternating potentialhaving a first and a second terminal and having a given voltage magnitude,

b. a plurality of vacuum tube filaments connected in a series path having a first terminal coupled to said first terminal of said source of AC potential, said plurality of vacuum tube filaments having a total impedance of a magnitude to develop a voltage thereacross less than said given voltage magnitude for a given series current flowing therethrough,

c. a transformer having a primary winding and a secondary winding, said primary winding coupled between said lower terminal of said AC source and the other terminal of said filament string to appear in series with said string, said primary winding having an impedance to provide a voltage drop thereacross approximately equal to the difference between said given voltage and said voltage across said filament string for said given series current, and

d. a kinescope tube also having a filament which, due to the characteristics of said tube, is to be operated relatively isolated from said plurality of vacuum tubes,

e. means coupling said filament of said kinescope tube across said secondary winding of said transformer, whereby said kinescope filament is further protected from transients which appear at said source of AC potential.

3. The combination according to claim 2 wherein:

a. said kinescopc filament requires for rated operation a current level in excess of the current rating of said vacuum tube filament series string, at a voltage level less than the voltage drop across said primary winding by a first ratio,

b. said transformer has a turns ratio between said primary and secondary windings for stepping down the voltage at said primary as transformed to said secondary winding whereby said given series current in said primary winding is transfonned at said secondary winding to a larger magnitude current, whereby said voltage and current applied to said kinescope are relatively equal to said rated levels.

4. The combination according to claim 2 wherein said second terminal of said source is coupled to a point of reference potential and therefore said primary winding has at least one terminal thereof at said point of reference potential.

5. The combination according to claim 2 also including:

a. impedance means in shunt with said primary winding for diverting a portion of said given series current around said primary winding and wherein:

b. said kinescope filament requires for rated operation a current level in excess of the current rating of said series filament string by a given ratio having a first magnitude, at a voltage level exceeded by the voltage level of said source by a ratio having a second magnitude,

c. said transformer having a turns ratio less than said second magnitude but greater than said first magnitude for stepping down the voltage at said secondary while stepping up the primary current not diverted by said impedance to said rated operation levels.

i t l 1 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,626, 242 Dated December 7, 1971 Invent Se vmour Reich It is certified that error appears in the above-identified patent and that 'said Letters Patent are hereby corrected as shovm below:

Column 2, line 63, that portion reading "lower" should read second Signed and sealed this 11th day of July 1972.

(SEAL) Attesb:

EDWARD M-FLETGHER, JR

ROBERT GOTTSCHALK Attesting Officer Gommis sioner of Patents FORM PO-1050 (10-69) USCOMM-DC 60376-P69 (LS. GOVERNMENT PRINTING OFFICE: 1969 O-356-334 

1. In a television receiver employing a plurality of vacuum tube circuits having the filaments of each of said vacuum tubes connected in series with one another between first and second terminals of a source of AC potential for energizing said filament string, said source having a voltage magnitude greater than that required by the voltage drop across said filament string, said receiver including a kinescope having a filament which desirably is isolated from said AC source, the improvement therewith comprising: a. a transformer having a primary winding and a secondary winding, said primary winding having an impedance so that the voltage developed thereacross is approximately equal to the difference between said voltage magnitude of said source and said voltage drop across said filament string, said primary winding being connected in series with said filament string, and b. means coupling said secondary winding of said transformer to said filament of said kinescope for energizing said filament while isolating said filament as desired due to said transformer action, whereby said kinescope filament is further protected from transients which appear on said AC source.
 2. In combination: a. a source of alternating potential having a first and a second teRminal and having a given voltage magnitude, b. a plurality of vacuum tube filaments connected in a series path having a first terminal coupled to said first terminal of said source of AC potential, said plurality of vacuum tube filaments having a total impedance of a magnitude to develop a voltage thereacross less than said given voltage magnitude for a given series current flowing therethrough, c. a transformer having a primary winding and a secondary winding, said primary winding coupled between said second terminal of said AC source and the other terminal of said filament string to appear in series with said string, said primary winding having an impedance to provide a voltage drop thereacross approximately equal to the difference between said given voltage and said voltage across said filament string for said given series current, and d. a kinescope tube also having a filament which, due to the characteristics of said tube, is to be operated relatively isolated from said plurality of vacuum tubes, e. means coupling said filament of said kinescope tube across said secondary winding of said transformer, whereby said kinescope filament is further protected from transients which appear at said source of AC potential.
 3. The combination according to claim 2 wherein: a. said kinescope filament requires for rated operation a current level in excess of the current rating of said vacuum tube filament series string, at a voltage level less than the voltage drop across said primary winding by a first ratio, b. said transformer has a turns ratio between said primary and secondary windings for stepping down the voltage at said primary as transformed to said secondary winding whereby said given series current in said primary winding is transformed at said secondary winding to a larger magnitude current, whereby said voltage and current applied to said kinescope are relatively equal to said rated levels.
 4. The combination according to claim 2 wherein said second terminal of said source is coupled to a point of reference potential and therefore said primary winding has at least one terminal thereof at said point of reference potential.
 5. The combination according to claim 2 also including: a. impedance means in shunt with said primary winding for diverting a portion of said given series current around said primary winding and wherein: b. said kinescope filament requires for rated operation a current level in excess of the current rating of said series filament string by a given ratio having a first magnitude, at a voltage level exceeded by the voltage level of said source by a ratio having a second magnitude, c. said transformer having a turns ratio less than said second magnitude but greater than said first magnitude for stepping down the voltage at said secondary while stepping up the primary current not diverted by said impedance to said rated operation levels. 